In literature, the word edition has several meanings. First, it can mean the form of a particular literary publication. For instance, Emma by Jane Austen can be published as a hard cover edition or a paperback edition.
Secondly, edition designates the various printings of a specific literary work. For instance, Emma was originally printed in 1816. All the copies of Emma that were printed in 1816 for the first time were the first edition.
Now, Bantam Publishers offers paperback copies of Emma in three editions: the 1969, 1981 and 2004 editions. The copy I repeatedly read is one of the thousands of books published in the 1981 Bantam edition.
A third usage of edition can mean how a literary work is formatted. For instance, the 1816 first edition of Emma was a three volume edition. This means that the story Emma was broken into three equal parts and each part, or edition, was published as a separate book within it's own binding.
Now only very large works like Will Durant's histories are separated into parts and published in individual bindings. You can see a picture of an 1816 first edition, three volume edition of Emma at TheWorldsGreatBooks.com.